Inside Out - S4-E17
Trivia: Skip's line in 'Inside Out' - 'Nobody comes back from paradise. Well, maybe a Slayer once,' is a reference to BTVS, and Buffy being brought back from heaven in the episode 'Bargaining'.
Trivia: In the episode "Orpheus," the actor who played the armed robber that shoots the cashier in the diner is played by Nate Dushku. He's the older brother of Eliza Dushku who also appears in the episode as Faith.
Trivia: To illustrate where her speech is placed on the itinerary, Fred compares it to a baseball player batting between Nomar Garciappara and Sammy Sosa, who both played with the Chicago Cubs. While Garciappara wouldn't join that team until well after the episode aired, and nobody could have known what would happen two years in the future, it's not a mistake; but as a Cubs fan, I find it an interesting choice of comparison.
Trivia: When Angelus taunts Connor about trying to kill him and then sleeping with Cordelia, he comments, "Screwing your mom and trying to kill your dad? There should be a play." This refers to the Greek tragedy "Oedipus," in which the eponymous character unwittingly marries his mother after killing his father.
Trivia: During the season's Angelus arc, a lot of David Boreanaz's dialogue was improvised.
Answer: Due to his epiphany, Angel basically had the 'true darkness' he worked so hard to reattain ripped away from him, like his soul was after sleeping with Buffy.